The bones associated with the skull including
the ear ossicles and hyoid bones.

The vertebral column that consists of 24
vertebrae, 1 sacrum and 1 coccyx.

The thoracic cage with 24 ribs and one sternum.

Functions of the Axial Skeleton

The axial skeleton forms a framework
for the organs of the ventral and dorsal body cavities. The
bones form an extensive surface area for muscle attachment. Many
bones contain red marrow that is involved in hemopoiesis.

Skull

The skull contains 22
bones of which 8 form the cranium that encloses
and protects the brain suspended in the cranial cavity and 14
facial bones that protect and support the digestive and
respiratory tracts.

The skull bones, with a few
exceptions, are connected by immovable joints called sutures. Some
of the major sutures are:

Lambdoid suture - between the occipital
and parietal bones. Sutural bones are often
found here.

Sagittal suture - between the parietal
bones.

Coronal suture - between the frontal and
parietal bones.

Squamous suture - between the parietal
and temporal bones.

Frontonasal suture - between the frontal
and nasal bones.

Bones of the Cranium

Occipital Bone

The occipital bone
contributes to the posterior, lateral and inferior surfaces of
the cranium. The following features are found on this bone:

foramen magnum - large circular
opening that connects the cranial and spinal
cavities.

occipital condyles - processes that
articulate with the first cervical vertebra.

styloid process - sharp
process near the mastoid process to which
ligaments and tendons attach.

stylomastoid foramen - opening
between the base of the styloid and mastoid
processes through which the facial nerve passes.

jugular fossa - depression
on the temporal bone that together with the
jugular notch of the occipital bone forms
the jugular foramen.

carotid canal - passageway
by which the internal carotid artery penetrates
the skull and reaches the brain.

foramen lacerum - jagged
opening between the temporal and
occipital bones. This is not an opening in
the living skull as it is closed by hyaline
cartilage.

internal acoustic meatus - canal
on the medial side of the petrous part
through which nerves and vessels supplying
the inner ear and the facial nerve pass.

Sphenoid

This complex bone
articulate with every other cranial bone. Although large, most
of the sphenoid is hidden by more superficial bones. The
sphenoid can be divided into the following parts:

Body

The body
is the central portion of the sphenoid. A
prominent feature of the body is the sella
turcica ("Turkish saddle") that
forms a bony enclosure around the pituitary
gland. The sella turcica can be divided into
the following parts:

hypophyseal fossa - depression
in which the pituitary gland rests
("seat of saddle").

The greater wings near their attachment to
the body have the following openings:

foramen rotundum - a
round opening.

foramen ovale - an
oval opening.

foramen spinosum - opening
where the greater wings form a sharp
process called the sphenoidal
spine.

Pterygoid Processes

Extending
downward on either side of the body are processes
called the pterygoid processes. These processes
form plates that permit muscle attachment. Pterygoid
canals are present at the base of these
processes.

Ethmoid

This irregular bone
forms part of the orbital complex, floor of the cranium, roof
of the nasal cavity, and part of the nasal septum. Features of
this bone include:

cribriform plate - superior surface
of the ethmoid perforated by olfactory foramina through
which the olfactory nerves pass.

crista galli - prominent ridge in
the middle of the cribriform plate and an attachment
point for the falx cerebri.

lateral masses - entire bony masses
attached on either side of the cribriform plate. The
lateral masses include:

mental foramina - openings for
nerves and blood vessels for the lower lip and
chin.

alveolar process - horseshoe-shaped
part that contains the roots of the lower teeth.

Orbital Complex

The orbits are the bony
recesses that enclose and protect the eyes. The orbital complex consists
of the bones that form the orbit and include the maxilla, lacrimal
bone, ethmoid, palatine bone, sphenoid, frontal bone and zygomatic
bone.

Nasal Complex

The nasal complex includes
all the bones that form the nasal cavity and paranasal sinuses.

Paranasal Sinuses

The paranasal
sinuses are air-filled chambers that are
connected to the nasal cavity. These sinuses are found
in the sphenoid, ethmoid, frontal bones and maxillae.
Functions of the sinuses include:

1. Lighten the skull.

2. Produce mucus.

3. Resonate during sound
production.

Hyoid Bone

The only bone in the body
that does not articulate directly with another. It lies
inferior to
the skull suspended by the stylohyoid ligament. Features
include:

body - central rectangular part of the
bone.

greater horns - large processes that
extend on either side of the body.

lesser horns - smaller processes that
extend on either side of the body.

The hyoid provides an
attachment surface for muscles and ligaments that stabilize and move
the tongue and larynx.

Skulls of Infants

The skull bones develop from
the fusion of multiple ossification centers. Until fusion, the
separate bones are attached by fibrous connective tissue. These
fibrous regions form the "soft spots" on the newborn's
head are are called fontanels.